37,097 research outputs found
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
Quarkonium Wave Functions at the Origin
We tabulate values of the radial Schr\"{o}dinger wave function or its first
nonvanishing derivative at zero quark-antiquark separation, for ,
, and levels that lie below, or just above, flavor
threshold. These quantities are essential inputs for evaluating production
cross sections for quarkonium states.Comment: 9 pages, RevTeX, no figure
Symplectic SUSY Gauge Theories with Antisymmetric Matter
We investigate the confining phase vacua of supersymmetric Sp(2\NC) gauge
theories that contain matter in both fundamental and antisymmetric
representations. The moduli spaces of such models with \NF=3 quark flavors
and \NA=1 antisymmetric field are analogous to that of SUSY QCD with
\NF=\NC+1 flavors. In particular, the forms of their quantum superpotentials
are fixed by classical constraints. When mass terms are coupled to
W_{(\NF=3,\NA=1)} and heavy fields are integrated out, complete towers of
dynamically generated superpotentials for low energy theories with fewer
numbers of matter fields can be derived. Following this approach, we deduce
exact superpotentials in and theories which cannot be
determined by symmetry considerations or integrating in techniques. Building
upon these simple symplectic group results, we also examine the ground state
structures of several and models. We
emphasize that the top-down approach may be used to methodically find dynamical
superpotentials in many other confining supersymmetric gauge theories.Comment: 21 pages, Revte
Polarization of Upsilon(nS) at the Tevatron
The polarization of inclusive Upsilon(nS) at the Fermilab Tevatron is
calculated within the nonrelativistic QCD factorization framework. We use a
recent determination of the NRQCD matrix elements from fitting the CDF data on
bottomonium production from Run IB of the Tevatron. The result for the
polarization of Upsilon(1S) integrated over the transverse momentum bin 8 < p_T
< 20 GeV is consistent with a recent measurement by the CDF Collaboration. The
transverse polarization of Upsilon(1S) is predicted to increase steadily for
p_T greater than about 10 GeV. The Upsilon(2S) and Upsilon(3S) are predicted to
have significantly larger transverse polarizations than Upsilon(1S).Comment: 15 pages, 3 figure
Magnetic Field Structure and Stochastic Reconnection in a Partially Ionized Gas
We consider stochastic reconnection in a magnetized, partially ionized
medium. Stochastic reconnection is a generic effect, due to field line
wandering, in which the speed of reconnection is determined by the ability of
ejected plasma to diffuse away from the current sheet along magnetic field
lines, rather than by the details of current sheet structure. We consider the
limit of weak stochasticity, so that the mean magnetic field energy density is
greater than either the turbulent kinetic energy density or the energy density
associated with the fluctuating component of the field. We consider field line
stochasticity generated through a turbulent cascade, which leads us to consider
the effect of neutral drag on the turbulent cascade of energy. In a
collisionless plasma, neutral particle viscosity and ion-neutral drag will damp
mid-scale turbulent motions, but the power spectrum of the magnetic
perturbations extends below the viscous cutoff scale. We give a simple physical
picture of the magnetic field structure below this cutoff, consistent with
numerical experiments. We provide arguments for the reemergence of the
turbulent cascade well below the viscous cut-off scale and derive estimates for
field line diffusion on all scales. We note that this explains the persistence
of a single power law form for the turbulent power spectrum of the interstellar
medium, from scales of tens of parsecs down to thousands of kilometers. We find
that under typical conditions in the ISM stochastic reconnection speeds are
reduced by the presence of neutrals, but by no more than an order of magnitude.Comment: Astrophysical Journal in pres
Phenomenological Theory of Superconductivity and Magnetism in HoDyNiBC
The coexistence of the superconductivity and magnetism in the
HoDyNiBC is studied by using Ginzburg-Landau theory. This
alloy shows the coexistence and complex interplay of superconducting and
magnetic order. We propose a phenomenological model which includes two magnetic
and two superconducting order parameters accounting for the multi-band
structure of this material. We describe phenomenologically the magnetic
fluctuations and order and demonstrate that they lead to anomalous behavior of
the upper critical field. The doping dependence of in
HoDyNiBC showing a reentrance behavior are analyzed
yielding a very good agreement with experimental data.Comment: 4 pages, 3 figures, REVTeX, submitted to PR
Deploying Trustworthy AI in the Courtroom: Lessons from Examining Algorithm Bias in Redistricting AI
Deploying trustworthy AI is an increasingly pressing and common concern. In a court of law, the challenges are exacerbated by the confluence of a general lack of expertise in the judiciary and the rapid speed of technological advancement. We discuss the obstacles to trustworthy AI in the courtroom through a discussion that focuses on the legal landscape surrounding electoral redistricting. We focus on two particular issues, data bias and a lack of domain knowledge, and discuss how they may lead to problematic legal decisions. We conclude with a discussion of the separate but complementary roles of technology and human deliberation. We emphasize that political fairness is a philosophical and political concept that must be conceived of through human consensus building, a process that is distinct from algorithm development
Color Reflection Invariance and Monopole Condensation in QCD
We review the quantum instability of the Savvidy-Nielsen-Olesen (SNO) vacuum
of the one-loop effective action of SU(2) QCD, and point out a critical defect
in the calculation of the functional determinant of the gluon loop in the SNO
effective action. We prove that the gauge invariance, in particular the color
reflection invariance, exclude the unstable tachyonic modes from the gluon loop
integral. This guarantees the stability of the magnetic condensation in QCD.Comment: 28 pages, 3 figures, JHEP styl
Curve classes on irreducible holomorphic symplectic varieties
We prove that the integral Hodge conjecture holds for 1-cycles on irreducible
holomorphic symplectic varieties of K3 type and of Generalized Kummer type. As
an application, we give a new proof of the integral Hodge conjecture for cubic
fourfolds.Comment: 15 page
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